Question 701190
D=RT
210=R*10 DOWNSTREAM.
R=210/10
R=21 MPH.
210=R*70 UPSTREAM
R=210/70
R=3 MPH. UPSTREAM.
(21+3)/2=24/2=12 MPH. FOR THE BOAT IN STILL WATER.
21-12=9 MPH. FOR THE CURRENT.
PROOF:
3+9=12
21-9=12